1. Field of the Invention
The invention relates to a vacuum coating unit to coat substrates on all sides by rotating the substrates in a material flow. The invention can be employed with various methods of vacuum deposition, including cathodic sputtering, ion plating, CVD (chemical vapor deposition), and other related methods.
2. Description of the Related Art
A method is known for providing substrates with a thin surface layer on all sides by subjecting them to a rotational movement within a directed vapor flow and/or by conducting them through the vapor flow while executing a rotational movement. For this purpose, the substrates can be individually mounted on shafts and brought into the vapor flow as the substrates rotate around the shaft axis. For the purpose of driving the shafts, coggears or rollers, which roll on a stationary toothed rack or rail, are affixed to the ends of the shafts. Resistance layers were already applied, in the indicated manner, on tubular insulators.
A method also is already known for affixing geometrically simple substrates, such as optical lenses and filters, on substrate holders and conducting them through a vapor flow while periodically executing complicated compound movements. Such devices or methods are suitable only for relatively small substrates whose profiling does not cause any problems with respect to a uniform layer thickness distribution.
For the purpose of vapor deposition onto relatively complicated parts, such as headlight reflectors for motor vehicle headlights, a method is already known for positioning the substrates on substrate holders which are arranged so they can rotate in an essentially cylindrical cage. The vaporizer source is located in the interior of the cage, so that, with one rotation of the cage, the substrates are moved through the vapor flow (which is directed upwards). The substrate holders then carry out an additional rotation within the cage because of a superimposed drive, which can be described as an involute movement. In this manner, a rather good layer thickness distribution is attained according to the law of chance. For extremely irregular shaped substrates of larger dimensions, however, which are to be subjected to vapor deposition in batches with high-melting metals or metal alloys, and wherein the substrate temperatures are to be above, for example, 555.degree. C., such a device is not suitable.
Substrates that are geometrically shaped in a particularly complicated manner, for which even greater importance is placed on a uniform layer thickness distribution, distribution of the alloy elements in the layer, and a great adhesive strength by intermetallic diffusion, are, for example, turbine buckets for gas turbines, as they are used in aviation. The problems connected with surface layers on such turbine buckets are described in the company publication "High Temperature Resistant Coatings for Super-Alloy" by Richard P. Seeling and Dr. Richard J. Stueber from the Chromalloy American Corporation, New York, USA. It has been extraordinarily difficult up to now to produce such substrates having layers with the required characteristics on a large industrial scale and at economically justifiable prices. Special problems associated with vapor deposition for substrates having geometrically complicated shapes are the transfer of a defined rotation from a driving motor to the substrate and the relatively high losses of expensive vapor deposition material, which does not condense on the substrate, but rather on the inside surfaces of the vapor deposition unit causing disruptive deposits. This problem can be counteracted by a spatially narrow arrangement of the substrate in the vapor flow or above the vaporizer crucible, but only to a certain extent.
A vapor deposition unit for the coating of substrates on all sides by rotating the substrates in a material flow also is known and is disclosed in West German Patent No. 2,813,180. This unit consists of a vacuum chamber with an elongated material source having a longitudinal axis and a transverse axis. The unit also has a substrate holder with several fasteners for the flat arrangement of several substrates above the material source. More specifically, the substrate holder has two parallel carrier arms arranged in the shape of a fork, whose longitudinal axes are arranged mirror-symmetrically to a vertical symmetric plane passing through the longitudinal axis of the material source. The substrate holder also has couplings for the substrates, which are arranged on the interior sides of the carrier arms set on one another. The rotation axes of the couplings are aligned vertical to the symmetric plane, and a driving shaft is correlated with each of the carrier arms in their longitudinal direction, each driving shaft being connected via angular gears with couplings, on the one hand, and with a motor, on the other hand.
Lastly, a device for the coating of three-dimensional substrates with comparatively large dimensions, such as gear rims for automobile tires, is known and disclosed in U.S. Pat. No. 5,558,909. In this device, two substrates are arranged on a carrier, which pivots in the coating chamber and which has a Z-shaped middle part bent at right angles. The substrates are mounted on shafts on one of the right-angle bends running at an incline with respect to the rotational axis of the carrier. The shafts, in turn, extend at right angles to this right-angle bend, and are held by the right-angle bend and driven by a motor. During the coating process, the substrate carrier rotates, whereby the substrates mounted on the shafts rotate around the substrate carrier axis and, further, rotate around their own inclined longitudinal axes.